1. Field of the Invention
This invention relates to improvements in a fuel injection carburetor in an internal combustion engine.
2. Description of the Prior Art
Recently, as one of fuel injection devices used in engines of motor vehicles, each of which is controlled by an electronic controller comprising a microcomputer, there has been known a fuel injection carburetor, which is a so-called single point injector, wherein a fuel injection valve is provided in an intake passage in a throttle body portion upstream of an intake manifold and fuel is injected at a portion upstream of a throttle valve provided in the throttle body.
In the case of the engine using the aforesaid fuel injection carburetor, in order to stabilize the idling operation of the engine, an idling bypass air passage is provided for leading air from an upstream portion of the throttle valve to a downstream portion thereof, bypassing the throttle valve.
In this case, when the engine is low in temperature, the atomization of fuel injected from the fuel injection valve is unsatisfactory. In consequence, it is necessary to supply a sufficient flow rate of bypass air from the bypass air passage and obtain a satisfactory air-fuel mixture.
Furthermore, the sliding friction is high in the engine when the temperature is low. Consequently, in order to stabilize the idle rotation, it is necessary to supply a required and sufficient flow rate of air to the engine.
Therefore, the higher the temperature of the engine rises, the less flow rate of bypass air passing through the bypass air passage should be supplied.
It is conceivable that, as the means for controlling the amount of bypass air passing through the bypass air passage, there may be provided a wax-type bypass air valve wherein the openings are varied in accordance with the engine coolant temperature.
However, such a disadvantage is presented in that case that, when the bypass air valve of the aforesaid wax-type is adapted to be driven in accordance with the engine coolant temperature, the openings of the bypass air passage become small excessively early, whereby the flow rate of bypass air necessary for the engine cannot be supplied, thus lowering the drivability.
The fuel sprayed from the fuel injection valve in the above-described fuel injection carburetor, depending on the throttle openings, flows down, going over an opening forward end at the upstream side of the throttle valve, or flows down only through the opening forward end on the downstream side of the throttle valve, and moves to the right and left in the throttle bore, whereby a dispersion may occur in the amount of distribution of fuel supplied to respective cylinders of a multi-cylinder engine.
There has been presented such disadvantages that, even if a bypass air passage is provided in the above-described fuel injection carburetor, the mixing becomes unstable because the air-fuel mixture in the intake passage as being a main passage and the bypass air flowing out of the bypass air passage meet with each other not at a constant ratio. Further, a high dispersion occurs in the air-fuel ratio in the respective cylinders in the multi-cylinder engine, whereby the engine output is adversely affected, the idle operation of the engine becomes unstable, and further, the response of the engine output to the variation in the openings of the throttle valve, i.e. the transient response, is unsatisfactory.
Further, in the fuel injection carburetor provided with the above-described idling bypass air passage, a bypass air passage for the idle adjustment having small diameter is provided in the intake passage, bypassing the throttle valve, from a position upstream to a position downstream of the throttle valve, in addition to the aforesaid idling bypass air passage, whereby the air flow rate in the bypass air passage controlled by the bypass air valve of the aforesaid wax-type is corrected by this bypass air passage for the idle adjustment.
In this case, an outlet of the bypass air passage for the idle adjustment should be opened at a position upstream of the intake manifold and downstream of the throttle valve, so that the outlet should necessarily be opened at a position downstream of the throttle valve and adjacent to the throttle valve in the intake passage of the throttle body.
However, the fuel injected through the fuel injection valve of the fuel injection carburetor is not perfectly atomized throughout all of the operating conditions of the engine, part of the fuel adheres to the inner wall of the intake passage of the throttle body, flows down together with the intake air stream, reaches the outlet of the bypass air passage for the idle adjustment provided adjacent the downstream side of the throttle valve, or the fuel injected through the fuel injection valve adheres directly to the aforesaid outlet and may intrude into the bypass air passage for the idle adjustment therefrom.
Such disadvantages have been presented that, when the liquid fuel adheres to the outlet of the bypass air passage for the idle adjustment or the liquid fuel intrudes into the bypass air passage as described above, the pressure in the vicinity of the outlet of the bypass air passage becomes unstable, with the result that the flow rate of air passing through the bypass air passage becomes unstable, and further, the liquid fuel, which has intruded into the bypass air passage, flows out into the throttle bore, whereby the idling operation of the engine becomes unstable.